A continuing goal of semiconductor processing is increased miniaturization while maintaining high performance. Modern semiconductor processes are heavily reliant on photolithography when preparing semiconductors to achieve this goal.
Photolithography typically involves the following steps. Initially, a layer of resist is formed over a substrate. A reticle/mask is subsequently placed above the resist and radiation is allowed to pass through openings of the reticle/mask and contact the resist in patterns defined by the reticle/mask. Depending on whether the resist is a negative resist or a positive resist, the radiation renders exposed portions of the resist more or less soluble in a solvent relative to unexposed portions. The solvent is subsequently utilized to remove the more soluble portions of the resist while leaving the less soluble portions as a patterned mask. The mask pattern can be transferred to the underlying substrate with a suitable etch. Exemplary methods of prior art photolithography and a problem therewith are illustrated in FIGS. 1-3.
Referring first to FIG. 1, a semiconductor substrate 1 at one stage of semiconductor processing is shown that includes a bulk substrate 3, multilayers 4 (e.g., conductive, semiconductive and/or insulative layers) and a resist 5. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Referring to FIG. 2, photoresist layer 5 has been processed to form masking blocks 7. It would be desirable that these masking blocks be of constant respective width in the illustrated cross-section from top to bottom. However in certain instances, the patterned photoresist tends to flare out at the bottoms/bases, as shown, forming what are commonly referred to as “footing”, depicted by feet 9.
Referring to FIG. 3, layers 4 have been etched using blocks 7 as an etch mask. As shown, feet 9 have functioned as part of that mask making the pattern of layers 4 substantially wider than the predominate width of blocks 7. In many instances, this is undesirable and/or difficult to predict or control.